heterotrophic stream system, can function with few plants. Plants, in a sense, are the energy driving force of an ecosystem, second only to the sun. The plants are of many types. Some grow for many years and are woody while others carry on their whole life cycle in a few weeks and survive only in a seed form. In the desert ecosystem both of these types are common. In addition, plants in the desert have adapted in many ways to drought or water stress conditions. These adaptations include, for example, deciduousness, small leaves, heavy pubescence on the leaves and succulence. For each plant species, the period of primary production varies. Some produce year around while others are seasonal. Any composition change in the plant species within an ecosystem may alter the periods and amounts of primary production. The organisms in an ecosystem that are dependent on the primary producers for energy are the animals and the decomposers. The animals that eat the plants (herbivores) are often referred to as secondary producers because the energy they store is available for the next trophic level, the carnivores. Animals play many roles in the transfer of energy through the ecosystem. These roles can be partly related to the types of animals, that is, whether they are large browsing or grazing mammals or small sap sucking or detritus eating invertebrates. Many of the animals also play an active role in the below ground portion of the ecosystem. In the desert ecosystem the larger animals are found in both the herbivore and carnivore levels. Some of the major herbivores are the lagomorphs (e.g., jack rabbits) and rodents (e.g., ground squirrels, wood rats and kangaroo rats). Insects such as grasshoppers also may play an important role in energy flow from plants to consumer. The carnivore consumer level varies widely from large carnivores, such as coyotes, to smaller vertebrates, such as the lizards and snakes, to small invertebrates such as beetles and spiders. Birds in the desert function in both herbivore and carnivore roles. Extremely important in the function of the desert ecosystem is the role of the detritivores, for example, termites. In order to have a constant energy and, nutrient turnover, primary and secondary production must be reduced to a form again usable to the primary producers. Often the dead organic and waste material is too large for rapid breakdown by decay organisms. The organisms that reduce the organic waste material and speed up the potential decay are the detritivores. These organisms are found both above and below ground.
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